p-Cresol is a specialty chemical with a market of 77 million pounds per year. It is primarily employed in the synthesis of antioxidants such as butylated hydroxytoluenes, and in the preparation of thermosetting resins such as Resoles and Novolacs. Though cresols can be obtained directly from naphtha fractions of coal and oil it is difficult to separate the meta and para isomers due to their very similar boiling points. To obtain pure p-cresol, toluene is sulfonated with sulfuric acid followed by fusion with sodium hydroxide to yield a slurry that is rich in the para isomer. A final cryogenic crystallization is employed to increase the purity of the p-cresol. Alternatively, toluene can be alkylated to a mixture of cymenes using propylene and a Lewis acid followed by dealkylation to cresol and a final cryogenic separation.
U.S. Pat. No. 2,437,648 describes a process for production of p-cresol which involves oxidation of toluene with hydrogen peroxide in the presence of a catalytically active metal oxide such as osmium tetraoxide.
U.S. Pat. No. 2,727,926 (U.S. Pat. No. Re. 24,848) describes a process which involves converting toluic acid to p-cresol in the presence of a soluble copper catalyst such as copper benzoate.
U.S. Pat. No. 3,046,305 describes a process for converting monoalkylbenzene compounds to p-alkylphenols and p-alkylbenzoic acids which involves reacting a monoalkylbenzene with phosgene to provide p,p'-dialkylbenzophenone, and thereafter reacting the p,p'-dialkylbenzophenone with hydrogen peroxide, acetic anhydride and sulfuric acid to yield p-alkylphenyl ester of p-alkylbenzoic acid, which intermediate is then hydrolyzed to the corresponding p-alkylphenol and p-alkylbenzoic acid products.
Other patents which are of general interest include U.S. Pat. Nos. 2,722,546; 2,903,480; 3,819,725; 3,929,911; 4,061,685; 4,189,602; 4,277,012; and the like; and British Pat. No. 964,980.
There is a continuing research effort to develop new and improved methods for the production of large volume specialty chemicals.
Accordingly, it is an object of this invention to provide a process for the production of p-cresol which is not energy intensive.
It is another object of this invention to provide a microbial metabolic pathway for the conversion of p-xylene to a p-cresol precursor.
Other objects and advantages of the present invention shall become apparent from the accompanying description and Examples.